"If D-Day failed, which it could have, we would have had the sad spectre of a revitalized German empire starting to build nuclear capacity," said Brinkley. "Fascism would have dominated the world, not democracy."

For those first agonizing hours of the invasion, Brinkley said, the success of D-Day hung in the balance.

Brinkley explained, "For the hours when this was happening, nobody knew what was really transpiring, but by the end of the day Franklin Roosevelt, our president, was able to hold a ceremony in the White House under a tree and say, 'We did it.""

Saving Private Ryan is a realistic and grim testimony to the nightmare the allied forces had to endure on the beaches of Normandy, Brinkley said.

"Steven Spielberg did a masterful historical recreation," said Brinkley. "It's almost stunning, the amount of detail he put into that.